Nonadherence to medical regimens is a pervasive and significant problem in chronic illness treatment affecting patient health and quality of life, clinical decisions, and health care costs. Approximately 50 percent of children and 65 to 75 percent of adolescent chronic illness patients are nonadherent. Studies have consistently shown that patient and family behavioral factors contribute to poorer adherence in children and adolescents. However, no standardized treatment protocol for nonadherence in adolescents exists. Multicomponent behavioral treatments that target patient and family factors have demonstrated significant improvements in adherence to medication in young children;however, research is needed to develop behavioral interventions targeting nonadherence in adolescents, particularly those with inflammatory bowel disease (IBD), as they are an understudied population with nonadherence rates as high as 62 percent. The long-term objective of this application is to provide a basis for continued development of effective treatments for nonadherence, particularly in pediatric IBD. The specific aim of the proposed research plan is to design a behavioral group treatment targeting medication nonadherence, and test the efficacy of this treatment in adolescents with IBD via a randomized controlled clinical trial. The intervention will use a multimethod assessment approach and integrate quantitative and qualitative data to target educational, organizational, and behavioral factors. We will test the hypotheses that the intervention will be feasible and acceptable, and that patients in the treatment condition will demonstrate improvement in medication adherence, disease functioning, and quality of life compared to patients in a usual care control condition. This application will advance the development of Dr. Kevin Hommel, a pediatric psychologist, as an independent investigator through a career development plan that includes 1) focused mentorship and collaboration with senior investigators, 2) didactic training in treatment outcome research, pharmacology, data analysis, health economics, and bioethics, 3) clinical and research training seminars, and 4) professional development activities. Relevance: Results of this research will contribute to public health by providing a basis for continued development of behavioral treatments for adolescent medical nonadherence. These evidence-based interventions should ultimately improve the effectiveness of health care and patient quality of life.